Modular fuel cell power system

ABSTRACT

A modular fuel cell power system includes a coolant source, a reactant source and a plurality of fuel cell modules. Each of the fuel cell modules includes a fuel cell stack and a fluid distribution plant in fluid communication with the reactant source, coolant source and fuel cell stack. The fluid distribution plant controls the flow of reactant between the reactant source and fuel cell stack. The fuel cell stacks are configured to be selectively electrically connected.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 12/355,451,filed Jan. 16, 2009, which is hereby incorporated by reference herein.

BACKGROUND

A fuel cell is an electrochemical conversion device that produceselectricity from a fuel and oxidant that react in the presence of anelectrolyte. A single fuel cell may include a membrane electrodeassembly and two flow field plates. Single cells may be combined into afuel cell stack to produce the desired level of electrical power.

A fuel cell may include two electrodes, an anode and cathode, separatedby a polymer membrane electrolyte. Each of the electrodes may be coatedon one side with a thin platinum catalyst layer. The electrodes,catalyst and membrane together form the membrane electrode assembly.

Gases (hydrogen and air) may be supplied to the electrodes on eitherside of the membrane through channels formed in the flow field plates.Hydrogen flows through the channels to the anode where the platinumcatalyst promotes its separation into protons and electrons. On theopposite side of the membrane, air flows through the channels to thecathode where oxygen in the air reacts with the hydrogen protons whichpass through the membrane.

The hydrogen dissociates into free electrons and protons (positivehydrogen ions) in the presence of the platinum catalyst at the anode.The free electrons are conducted in the form of usable electric currentthrough an external circuit. The protons migrate through the membraneelectrolyte to the cathode. At the cathode, oxygen from the air,electrons from the external circuit and protons combine to form waterand heat.

SUMMARY

A power system includes a coolant source, a reactant source, and aplurality of self-contained fuel cell modules. Each of the modulesincludes a fuel cell stack and a fluid distribution plant disposedtherein, the fluid distribution plant is in fluid communication with thereactant source, coolant source and fuel cell stack and is configured tocontrol flow of reactant between the reactant source and fuel cellstack. The fuel cell stacks are configured to be selectivelyelectrically connected.

An automotive power system includes a plurality of self-contained fuelcell modules. Each of the modules includes a fuel cell stack, a fluiddistribution plant in fluid communication with the fuel cell stack andconfigured to control flow of reactant and air to the fuel cell stack,and an electrical switch electrically connected with the fuel cellstack. The electrical switches are arranged to selectively electricallyconnect at least some of the fuel cell stacks.

While example embodiments in accordance with the invention areillustrated and disclosed, such disclosure should not be construed tolimit the invention. It is anticipated that various modifications andalternative designs may be made without departing from the scope of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an embodiment of a fuel cell module.

FIG. 2 is a block diagram of an embodiment of a modular fuel cell powersystem.

DETAILED DESCRIPTION

Referring now to FIG. 1, an embodiment of a fuel cell module 10 (whichmay be disposed within a vehicle, but, of course, may be used outside ofa vehicle in other embodiments) includes a fuel cell stack 12 and fluiddistribution plant 14. As known in the art, the fuel cell stack 12includes a plurality of fuel cells (not shown). Each of the fuel cellsincludes an anode 16 and cathode 18 schematically depicted within thefuel cell stack 12. The anodes 16 and cathodes 18 are cooled by acoolant in a coolant line 20. As described in detail below, the fluiddistribution plant 14 distributes hydrogen to the anodes 16, air to thecathodes 18 and coolant to the fuel cell stack 12.

The fluid distribution plant 14 of FIG. 1 may include a supply valve 22,pressure control valve 24, flow combiner 26, recirculation blower 28,water separator 30, filter 32 and purge/drain valve 34. Hydrogen from anon-board hydrogen source 36, e.g., a pressurized hydrogen tank, flowsthrough the supply valve 22 to the pressure control valve 24. Thepressure control valve 24 controls the pressure of the hydrogen flowingout of the valve 24. The pressure controlled hydrogen then flows throughthe flow combiner 26, described below, and to the anodes 16 of the fuelcell stack 12.

Un-reacted hydrogen and water vapor may flow out of the fuel cell stack12 and into the water separator 30. The water separator 30 separates thewater vapor from the un-reacted hydrogen. The water vapor may then passthrough the filter 32 and be removed from the fuel cell module 10 viathe purge/drain valve 34.

The recirculation blower 28 may move the un-reacted hydrogen to the flowcombiner 26. The flow combiner 26 may then combine the un-reactedhydrogen with hydrogen from the hydrogen source 36 for delivery to thefuel cell stack 12.

The fluid distribution plant 14 of FIG. 1 may also include a compressorcontroller 38, motor/compressor 40, intercooler 42, humidifier 44,by-pass valve 46 and throttle valve 48. Air from an ambient air source50 flows through the motor/compressor 40, under the control of thecompressor controller 38, and to the intercooler 42. The intercooler 42may cool the air to the appropriate temperature, in a known fashion,before delivery to the cathodes 18 of the fuel cell stack 12 by way ofthe humidifier 44 and/or by-pass valve 46. As apparent to those ofordinary skill, the humidifier 44 may appropriately humidify the air ina known fashion. The by-pass valve 46 may be actuated topartially/completely by-pass the humidifier 44 as conditions dictate.

Air may flow out of the fuel cell stack 12, through the humidifier 44and be exhausted via operation of the throttle valve 48.

The fluid distribution plant 14 of FIG. 1 may further include a floworifice 52. Coolant from an on-board coolant source 54 may flow throughthe flow orifice 52 prior to delivery to the intercooler 42 to alter theflow rate and/or pressure of the coolant. Coolant from the on-boardcoolant source 54 may also flow through the fuel cell stack 12 to absorband carry away heat generated by the electrochemical reaction takingplace within the fuel cell stack 12. Coolant from the fuel cell stack 12and intercooler 42 may be directed to an on-board coolant return 56,e.g., a fluidic coupling on-board the vehicle which connects to any mainand/or auxiliary cooling system(s).

In other embodiments, the fluid distribution plant 14 may have othersimilar configurations. For example, an ejector or ejector system mayreplace the flow combiner 26 and hydrogen blower 28; a contacthumidifier or entropy wheel may replace the gas-to-gas humidifier 44;by-pass valve 46 may be deleted; water may be injected into thecompressor 40 for cooling thus replacing the intercooler 42; thepurge/drain valve 34 may be replaced by individual valves, etc.

In the embodiment of FIG. 1, the fuel cell module 10 may include ananode pressure sensor 58, cathode pressure sensor 60, coolanttemperature sensor 62 and voltage and current sensors 64, 66. Thesensors 58, 60 detect the pressures associated with the anodes 16 andcathodes 18 respectively. The sensor 62 detects the temperature ofcoolant in the coolant line 20. The sensors 64, 66 detect a voltage andcurrent respectively associated with the fuel cell stack 12.

The fuel cell module 10 may also include valve position sensors 68, 70.The position sensor 68 detects the position of the by-pass valve 46. Theposition sensor 70 detects the position of the throttle valve 48. Thefuel cell module 10 may further include a temperature sensor 72,hydrogen sensor 74, water level sensor/switch 76 and speed and currentsensors 78, 80. The sensor 72 detects the temperature of air exiting thefuel cell stack 12. The sensor 74 detects the presence of hydrogenwithin the fuel cell module 10. The water level/switch 76 detects thelevel of water within the water separator 30. The speed and currentsensors 78, 80 detect a speed and current respectively associated withthe compressor controller 38.

As apparent to those of ordinary skill, information collected by atleast some of the sensors 58 through 80 may be used by a controller (notshown) to control, for example, the fuel distribution plant 14. As anexample, pressure information detected by the pressure sensor 58 may beused to control the operation, in a known fashion, of the supply valve22, pressure control valve 24, flow combiner 26, etc. As anotherexample, pressure information detected by the pressure sensor 60 may beused to control the operation, in a known fashion, of the compressorcontroller 38, motor/compressor 40, etc. Other control scenarios are, ofcourse, also possible. In embodiments having more than one fuel cellmodule 10, each may have its own controller or may share a commoncontroller. Any suitable arrangement, however, may be used.

The fuel cell stack 12 and compressor controller 38 of FIG. 1 areelectrically connected with a high voltage bus (not shown). As apparentto those of ordinary skill, energy output by the fuel cell stack 12 andprovided to the high voltage bus may, for example, be stored in a powerstorage unit (not shown) or used to generate motive power via anelectric machine (not shown).

Referring now to FIG. 2, numbered elements that differ by 100 relativeto the numbered elements of FIG. 1 have similar descriptions to thenumbered elements of FIG. 1. An automotive vehicle 108 includes aplurality of fuel cell modules 110. Each of the fuel cell modules 110includes a fuel cell stack 112 and fluid distribution plant 114. Each ofthe fluid distribution plants 114 receives hydrogen, air and coolantfrom a hydrogen source 136, ambient air source 150 and coolant source154 via a common set of supply lines 182, 184, 186 respectively.

In the embodiment of FIG. 2, the fluid distribution plants 114 arearranged in parallel relative to the sources 136, 150, 154. In otherembodiments, however, the fluid distribution plants 114 may be arrangedin series relative to the sources 136, 150, 154. In still otherembodiments, each of the fluid distribution plants 114 may receivefluids from the sources 136, 150, 154 via a dedicated set of supplylines. Other configurations are also possible. Valves (not shown) mayalso be positioned within the flow path of the supply lines 182, 184,186. In such embodiments, fluid supply from the sources 136, 150, 154 toany one of the fluid distribution plants 114 may be selectively turnedon or off.

The fluid distribution plants 114 exchange hydrogen, air and coolant (asindicated by arrow) with the fuel cell stacks 112 in a manner similar tothat described with respect to FIG. 1.

Return lines 188, 190, 192 form a return loop through the fluiddistribution plants 114 for each of the hydrogen, air and coolantrespectively. The return line 188 of FIG. 1 is configured tore-circulate hydrogen back to the supply line 182 in a known fashion.The return line 190 for the air is exhausted to the exterior of thevehicle 108. The return line 192 for the coolant provides the coolant toa coolant return 156. Any suitable fluidic configuration, however, maybe used.

Each of the fuel cell modules 110 of FIG. 1 also includes switches 194,196. In other embodiments, the switches 194, 196 may reside outside ofthe fuel cell modules 110 in any suitable location. Each of the switches194 is associated with a negative side of one of the fuel cell stacks112. Each of the switches 196 is associated with a positive side of oneof the fuel cell stacks 112. The switches 194, 196, of course, may takeany suitable form.

To facilitate discussion, each of the switches 194, 196 has a terminallabeled “A” and a terminal labeled “B.” As explained in detail below,each of the fuel cell stacks 112 may be electrically connected inseries, parallel or by-passed through operation of the switches 194,196.

As illustrated in FIG. 2, the switches 194, 196 are configured toelectrically connect the fuel cell stacks 112 in parallel. That is,positive terminals of each of the fuel cell stacks 112 are electricallyconnected together via the switches 196 and negative terminals of eachof the fuel cell stacks 112 are electrically connected together via theswitches 194. As apparent to those of ordinary skill, the switches 194,196 may also be configured to electrically connect the fuel cell stacks112 in series via the respective “A” terminals (except, of course, forthe switch 194 associated with left most illustrated fuel cell module112 whose switching configuration would remain the same.) As apparent tothose of ordinary skill, certain switches 194, 196 may be configured toelectrically by-pass certain of the fuel cell stacks 112. As discussedabove, the electrical output of the fuel cell stacks 112 may be storedin a power storage unit (not shown) or used to generate motive powervia, for example, an electric machine (not shown).

In certain embodiments, the fuel cell stacks 112 and fluid distributionplants 114 may be selectively by-passed through the control of thevalves (described above) associated with the supply lines 182, 184, 186and the switches 194, 196. As apparent to those of ordinary skill, thiscontrol may be performed by a controller (not shown) in communicationwith the valves and switches 194, 196. Such by-passing may be performedto bring the fuel cells modules 110 on and/or off line as conditionsdictate. As an example, a low driver demand for power may require onlythe operation of a single fuel cell module 110. Any other fuel cellmodules 110 may be taken off line. As another example, a fuel cellmodule 110 experiencing an operational issue may be taken off line. Asyet another example, high driver demand for power may require theoperation of all fuel cell modules 110.

References to hydrogen as noted herein generally includes hydrogen-richgases such as reformates. In addition, the oxygen in the airstream mayinclude various types of oxygen generated by oxygen enrichment methods.While embodiments of the invention have been illustrated and described,it is not intended that these embodiments illustrate and describe allpossible forms of the invention. Rather, the words used in thespecification are words of description rather than limitation, andvarious changes may be made without departing from the spirit and scopeof the invention.

What is claimed is:
 1. A power system comprising: a coolant source; areactant source; and a plurality of self-contained fuel cell moduleseach including a fuel cell stack and a fluid distribution plant disposedtherein, the fluid distribution plant in fluid communication with thereactant source, coolant source and fuel cell stack and configured tocontrol flow of reactant between the reactant source and fuel cellstack, the fuel cell stacks configured to be selectively electricallyconnected.
 2. The system of claim 1 wherein the fluid distributionplants further control flow of air to the respective fuel cell stacks.3. The system of claim 2 wherein the fluid distribution plants eachinclude a humidifier to humidify the air prior to the air entering therespective fuel cell stacks.
 4. The system of claim 2 wherein the fluiddistribution plants each include an intercooler to cool the air prior tothe air entering the respective fuel cell stacks.
 5. The system of claim1 wherein the fluid distribution plants each include a pressure controlvalve to control a pressure of the reactant from the reactant source. 6.The system of claim 1 wherein the fuel cell stacks are furtherconfigured to be selectively electrically connected in parallel duringcertain periods and series during other periods.
 7. The system of claim1 wherein each of the fuel cell modules includes at least one electricalswitch and wherein the fuel cell stacks are selectively electricallyconnected via the electrical switches.
 8. An automotive power systemcomprising: a plurality of self-contained fuel cell modules eachincluding a fuel cell stack, a fluid distribution plant in fluidcommunication with the fuel cell stack and configured to control flow ofreactant and air to the fuel cell stack, and an electrical switchelectrically connected with the fuel cell stack, the electrical switchesarranged to selectively electrically connect at least some of the fuelcell stacks.
 9. The system of claim 8 wherein the electrical switchesare further configured to selectively electrically connect at least someof the fuel cell stacks in parallel during certain periods and seriesduring other periods.
 10. The system of claim 8 wherein the fluiddistribution plants each include a humidifier to humidify the air priorto the air entering the respective fuel cell stacks.
 11. The system ofclaim 8 wherein the fluid distribution plants each include anintercooler to cool the air prior to the air entering the respectivefuel cell stacks.
 12. The system of claim 8 wherein the fluiddistribution plants each include a pressure control valve to control apressure of the reactant.